Method and apparatus for controlling periodically reversed heat exchange devices



P. K. RICE ET AL May 4, 1954 2 Sheets-Sheet 1 Filed Nov. 10, 1950 J fl MI\ Z 4 BA e 4 4 p 4. 5 MA g v .sttvfimum INVENTORS -PH|LIP K. RICEWILLIAM G.TUEL 9' ATTORNEY K RICE ET AL 2,677,252

May 4, 1954 P METHOD AND APPARATUS FOR CONTROLLING PERIODICALLY REVERSEDHEAT EXCHANGE DEVICES Filed Nov. 10, 1950 2 Sheets-Sheet 2 I INVENTORSlP K. RiCE IAM G. TUEL ATTORNEY Patented May 4, 1954 METHOD ANDAPPARATUS FOR CONTROL- LING PERIODICALLY REVERSED HEAT EXCHANGE DEVICESPhilip K. Rice, White Plains, and William G, Tuel, Kenmore, N. Y.,assignors to Union Carbide and Carbon Corporation, a corporation of NewYork Application November 10, 1950, Serial No. 195,102

Claims. 1

This invention relates to a method of and apparatus for controlling theoperation of periodically reversed heat exchange devices employed foreffecting heat exchange between gaseous fluids, particularly when thegaseous fluid to be cooled contains condensible material.

Heat exchangers of the passage exchanging type and cold accumulators orregenerators are employed for cooling gaseous fluids by therefrigeration gases. to be warmed. Such heat exchange devices areparticularly useful when the gaseous fluid to be cooled containscondensible material, which condensible material is deposited on theheat exchange surfaces from the gaseous fluid, when it passes throughone of a pair of such heat exchange passages.

The outflowing gas to be warmed is initially free of such condensiblematerial and is passed outward through the other of the pair ofpassages. During such outflow, the gas to be warmed effects evaporationof the condensible material that was deposited when that passage wasused to cool inflowing gaseous fluid. The volume of the outilowing gasis larger than the volume of the infiowing gaseous fluid which depositsthe condensiblc material. For example, a process for the liquefactionand rectification of air to provide oxygen and nitrogen containingfractions may employ passage exchanging heat exchangers or coldaccumulators to efiect the heat exchange between the incoming air andthe nitrogen and oxygen products leaving the system and since theinflowing air is under pressure, its volume is smaller than the volumeof outfiowing products.

Water vapor, carbon dioxide, and hydrocarbons are frozen out of the airand deposited on the heat exchange surfaces. The air flows in throughone passage or ccumulator while the nitrogen, for example, flows outwardthrough the other passage or accumulator. The flows are periodicallyreversed, so that the nitrogen which flows out through a passage oraccumulator through which the air had previously flowed, evaporates thedeposited condensible material. The operation of cold accumulators orregenerators is described in United States Patent No. 1,970,299 of M.Frankl.

The reversing passage heat exchanger referred to herein is one in whichthe air and an outgoing product may flow simultaneously through twopassages which are in heat exchanging relation to each other. Such heatexchanger may also have one or more nonreversing passages through whichanother product or products flow 2 constantly. Two sets of the reversingpassages are provided, and the flow through such passages isperiodically reversed so that for one halfperiod of the reversing cycle,air will flow inward through one of the passages while outflowingproduct flows outward through the other of the passages, and during theother half-period of the reversing cycle, the air will flow inwardthrough the other passage while the outfiowing product flows through thefirst-mentioned passage. Such type of heat exchanger is useful when itis desired that the outfiowing gas which passes through the nonreversingpassage should not be contaminated by impurities and diluted by ,aresidue of the incoming gas to be cooled.

If the flow of the outgoing product through a cold accumulator could bebalanced correctly and precisely against the flow of air during thepreceding half -perio.d, the deposit-ed materials would be completelyremoved. In practice it has been found, however, that one of theaccumulators may have a slightly higher pressure drop or resistance toflow therethrough than the other of a pair (owing perhaps to a slightlygreater packing density), or that operational variations may slightlydecrease the flow of nitrogen through one of the accumulators of apairso that insufiicient nitrogen may be available to remove com.- pletelythe deposited material, particularly the carbon dioxide deposits whichare more diflioult to remove due to the lower vapor pressure of carbondioxide in the colder regions of the accumulator. Then in the succeedingair flow period additional deposits of condensible material are made andthe pressure drop that creates resistance to nitrogen flow becomesslightly further increased so that even less of the carbon dioxide isremoved. Even with perfectly balanced flows such cumulative action oncestarted may cause one regenerator of a pair to become plugged, and it isnecessary to completely shut down operation to thaw out the pluggedregenerator. This p1ugging of the regenerators may occur even though thereversing periods are carefully adjusted to be equal and the resistanceto gas fiow to and from the regenerator passages are adjusted andbalanced.

It has been proposed to provide spare full-size regenerators so thatwhen one regenerator of a group becomes clogged, the clogged,regenerator would be removed from service and thawed while the spareregenerator would be substituted to continue operation. Such solution isquite uneconomical.

A pr n ipal object of the present invention is therefore to provide animproved method of and apparatus for controlling the operation ofperiodically reversed heat exchange devices employed for effecting heatexchange between gaseous fluids. More specifically it is an object ofthe present invention to provide a method of and apparatus forpreventing excess accumulation of condensible material in periodicallyreversed heat exchange devices such as cold accumulators, regenerators,or passage exchanging heat exchangers employed for cooling the gaseousfluid containing such material by a cold gas that is initially free ofsuch material. A further object is to provide a method of and apparatusfor controlling the operation of cold accumulators or regenerators usedfor cooling atmospheric air by the refrigeration of outflowing productsof the low temperature separation of air so as to prevent gradualclogging of one or the other of a pair of regenerators by incompletelyvaporized carbon dioxide.

These and other objects and advantages of the invention will becomeapparent from the following description and the accompanying drawings,in which:

Fig. 1 is a diagrammatic view of an exemplary apparatus for controllingthe operation of a pair of cold accumulators or regenerators accordingto the invention;

Fig. 2 is a fragmentary diagrammatic view of a portion or" thecontrolling apparatus employing electrically-operated valves instead ofpressureoperated valves;

Fig. 3 is a diagrammatic view of apparatus at the cold end ofregenerators for controlling flow according to the invention; and

Fig. 4 is a diagrammatic view of apparatus for controlling flow to a setof four regenerators according to a further aspect of the invention.

It has now been found that the problem of clogging of heat exchangerpassages can be solved by operating the heat exchange system in a mannerwhich deliberately unbalances the periodic cycle of air and outgoingproduct flow. This unbalance is effected so as to pass an excess of onegas through one heat exchange passage of a pair over that passed throughthe other or" such pair until a tendency to clog is indicated and theneffecting an opposite unbalance to clear the clogging passage. Apreferred way of effecting such unbalance according to the inventionmakes the period of the reversing cycle for air flow unequal to theperiod for flow of outfiowing separation product. Thus, according to theinvention, the reversal period is controlled so that for an indefiniteperiod of operation the time periods for flow of air are greater thanthe time periods for flow of product for one of a pair of accumulators,the converse being true of the other accumulator. Such unbalancedoperation is continued until measurements of pressure drop indicate thatcondensible material is tending to build up in the one accumulator. Thenthe operation is deliberately unbalanced in the opposite sense to causethe flow of more air and less product alternatively through the other ofthe pair of accumulators, which will then reduce or clear out theaccumulation of condensible material in the one accumulator. Whencondensible material tends to clog said other accumulator the operationis unbalanced in the initial direction.

For example, in air separation, wherein air is cooled against outfiowingnitrogen product by a pair of regenerators N-i and N-Z, we may assumethat regenerator N-l is indicating an increasing pressure drop due tocarbon dioxide accumula tion. If we assume that the complete reversingcycle period is five minutes, the normal or customary time for nitrogenflow through regenerator l-l-i or N-Z would be two minutes and thirtyseconds, while the normal time for air flow through regenerator N-2 orN-i would also be two minutes and thirty seconds. According to theinvention, the nitrogen flow through regenerator l is increased slightlyby from 2 to 10 seconds, for example, to two minutes, thirty-fiveseconds, while the air flow period through regenerator N-i is decreasedto two minutes, twentyfive seconds. The excess of nitrogen which thenpasses through regenerator N-i during the nitrogen fiow periods willremove the accumulated deposits. Such unbalanced operation, however,causes the nitrogen flow period for regenerator N-Z to be only twominutes, twenty-five seconds, while the air flow time throughregenerator N4 is two minutes and thirty-five seconds. Eventually suchoperation, after a number of reversals, causes accumulated deposits toincrease in regenerator N-2. Then the reversing cycle is unbalanced inthe opposite direction so that the nitrogen flow through regenerator N-2is increased to two minutes, thirty-five seconds while the air flowthrough regenerator N-2 is shortened to two minutes, twenty-fiveseconds. Operation continues in this manner until regenerator N-iindicates an increasing pressure drop, whereupon the unbalance is againreversed.

The two regenerators of a pair are thus deliberately operated in amanner alternately causing deposits in the one and excess clearing ofdeposits in the other. Theoretically a regenerator system should notclog if the outgoing product and air flows are in perfect balance. Inpractice this ideal is not attained, since the regenerators of a pairmight not have identical characteristics, and even if they wereidentical, operational variations can cause them to become unbalanced.Furthermore, deposits of solid material can create greater fiowresistance in one regenerator than in the other to initiate a cumulativeclogging effect. It is contemplated that this deliberate unbalancing inthe correct direction when required may be effected by manual or byautomatic response to pressure drop measurements.

Alternatively it is contemplated that the deliberate unbalance may beeffected while keeping the reversal period times constant and eitherincreasing the resistance to flow of the air, for example, intoregenerator N-i over that into regenerator N-Z, or increasing flowresistance to entrance of outgoing nitrogen to regenerator N-Z over thatto regenerator N-l, such unbalance being maintained until regeneratorN-Z begins to clog; then deliberately unbalancing the flows byrestriction oppositely for a succeeding period of operation. If thetotal reversal period is short such operation will not affect thepressures seriously because there will usually be adequate volume in thepiping or the requisite surge chamber volume may be provided.

Usually the air is compressed by compressor devices such as a rotarycompressor, the output volume of which is affected by the head pressure,and therefore, the increased flow resistance when applied to theincoming air, reduces the flow volume. With a constant volumecompressor, a surge chamber of suitabl volume according to the one-halfreversing period time employed could be provided.

ihe method according to the invention thus operate broadly consists incausing the flow of more of a gaseous fluid and less of a cold gasalternately through one of a heat exchange passage pair than through theother of said pair until condensible material tends to clog the onepassage, then causing the flow of more of the gaseous fiuid and ess ofthe cold alternately through the other of said passages to reduce theaccumulation of condensible material in the one passage, and whencondensible material tends to clog said other passage, repeating thefirst step.

Referring now to the drawings, and particularly to Fig. 1, the inventionis illustrated by an embodiment of apparatus adapted to control thereversible operation of a pair of regenerators N-I and N-2 used to cooland condition air by an outflowing product of air separation, such asthe nitrogen product by alteration of the flow time periods.

Air under a relatively low pressure, for example, 75 p. s. i., issupplied through a conduit It to branches Ii and 12 which connectconduit in to the warm end of the regenerators N-l and N-2. The cooledair alternately leaves the cold end of the regcnerators through conduitsi3 and I5 which join an air delivery conduit I5. The nitrogen product issupplied through a conduit it connected to branches i! it that conductthe nitrogen to the cold ends of the regenerators N-! and N-E. Thewarmed nitrogen flows from the regenerators through branch conduits itand 28 that connect to a discharge conduit 2!. The conduits associatedwith the warm ends of the regenerators are controlled by reversingvalves which preferably are stop valves that are motor operated, forexample, by fluid pressure or by electrically responsive means. Thusconduit i i has therein. a iiuid pressure operated stop valve 22. Thebranch conduit i2 is controlled by a similar reversing valve 23, whilethe branches i9 and for nitrogen are controlled by reversing valves 24and 25. The connections associated with the cold end of the regeneratorsare preferably supplied with automatically operated nonreturn valves orcheck valves indicated at 26, 2'5, and 29 interposed in the respectivebranches :5, as, i1, and E3. The check valves 26 and 2'! are arranged topermit outflow only of air from regenerator N-l or N-'2 while the check.valves is and :29 are arranged to permit inflow only of nitrogen to theregenerators N-! or N--2.

The motor elements of the reversing valves are supplied with timedpressure impulses obtained from a source of fluid pressure which, forexample, may oe a compressed air supply provided through a manifoldconduit as. To this end there is provided a constant speed motor device'31 which may be a synchronous motor-driven speed reducer constructed toturn a cam shaft, indicated by broken center line 32, at a desired speedproviding a complete revolution for each complete reversing cycleperiod. For example, the cam shaf may make one turn in five minutes. Theearn shaft 32 carries a series of cams 11-1, 13-5, A-i, B-.2, A-S, 13-3,A-4, and 13-4. The cams are provided with high and low cam surfaces 34and 35 against which cam followers 38 engage. The cam followers areoperatively connected to stop valves 31 of which there is one for eachcam. The stop valves 31 are connected by conduits 38 to the air pressureline 35, and the outlets of the stop valves 31 are connected by conduits39 'and 40 to two-way valves, there being a two-Way valve 41 to receivethe pressure impulse "from one or the other of the stop valvesassociated with cams A-l and 3-4, a two-way valve 42 connected toreceive the pressure impulses from the valves operated by cams A-2 and3-2, a two-way valve 43 connected to receive pressure impulses fromvalves operated by cams A-3 and 13-3, and a twoway valve 44 connected toreceive pressure impulses from stop valves operated by cams A-4 and B-4.The two-way valve ll has its common outlet connected to a conduit 45connected to deliver the pressure impulse to the reversing valve 22.Similarly two-way valves 52, 43, and 44 have their common outletsconnected by conduits 46, 4?, and 48 to deliver pressure impulses to thereversing valves 24, 25, and 23 respectively. The two-way valves 4 l,42, 43, and 44 may have their operating handles connected together forsimultaneous operation, as indicated by the broken line 49.

It will be noted that in one position or" the valves ii to 44 inclusivethe reversing valves of the regenerators are connected for operation tothose valves 31 which are controlled by the cams A-l to A-4 inclusive,and when the valve-operating means 49 is shifted to the right, thevalves 4| to 44 inclusive will connect the regenera'tor reversing valveswith those valves 5! which are controlled by the cams 13-! to 13-4inclusive.

- While all of the cams rotate at the same speed,

the length of high cam surface 35 of half or" the cams is longer thanthe length of the high cam surface 3d of the rest of the cams. Thus tooperate the reversing valves on the cycle timing mentioned hereinaboveas an example, all the cams will make one revolution every five minutesand, with respect to the cams A, the length of the high part '84 of camA--! will be equivalent to 155 seconds, so as to keep the air flowinginto regenerator N-i for 155 seconds of the time cycle. The cam A-Zshould then have a length of high surface 36 equivalent to seconds, sothat the time of nitrogen flow will be 145 seconds. t should be noted,however, that the relation of the valve 37 with respect to the cam A-land the relation of the valve 31 with respect to the cam A-2 is suchthat the valve follower 35 for cam A-Z rides on the low side 35 of thecam, while the follower 35 for the cam A-i rides on the high side 34 ofthat cam, and vice versa. lIher-efore reversing valves 22 and 24 cannever be simultaneously opened. For the cams A-3 and A-4, the high side35 of cam A-3 will be similar to cam A-i, providing an opening time ofseconds for nitrogen, while the high side of cam A-4 will be similar tocam A-2 and provide an opening time of 145 seconds, so that forregenerator N-2 the time of nitrogen flow is 155 second and for air flowis 145 seconds, and the cam relation is such that when the air is on forregenerator N-i, the air is off for regenerator N-Z.

The cams B are arranged so that the high side 3 30f cam 13-! isequivalent in length to 145 seconds 'to provide an air flow time of 145seconds for regen'erator N-i while the cam B-z has a length of high side3-2 equivalent to 155 seconds to provide 155 seconds of nitrogen flow.Cam El-'3 has a length of high surface 34 equivalent to 145 seconds toprovide 145 seconds of nitrogen flow for regenerator N-Z, while the cam13-4 has a length of high surface 34 of 155 seconds to provide an airfiow to regenerator N-2 of 155 seconds. Cams B are also arranged so thatfor either regenerator, air flow is off when nitrogen flow is "on, andvice versa, and also so that when air flow is on for one regenerator, itis off for the other regenerator.

A convenient way to determine when a regenerator is tending to becomeclogged is to measure the pressure drop through the regenerator. Suchpressure drop measurement can be taken during the period of air flow orduring the period of nitrogen flow, and since the nitrogen pressure islower, it may be preferable to take the measurement during the nitrogenflow period. To this end there may be provided diiferential pressuregauges ii and 52, the gauge being connected by conduits 5D and 53 withthe ends of regenerator N-I, and the gauge 52 being connected byconduits 54 and 55 with the ends of regenerator N-E.

In operation, the pressure readings of the gauges 5! and 52 for therespective nitrogen flow periods are read and compared, and when it iseen that the pressure drop through regencrater N-i, for example, isconsistently becoming greater the pressure drop through regenerator N-2,the valves ll to is inclusive would be shifted to the right to place thereversing valves 22, 2 3, and 25 under the control of the cams B. '1 hiswill cause the air-on time for regenerator l l-i to be 145 seconds, andthe nitrogen flow time for regenerator N-I to be 155 seconds, while theair-on time for regenerator N-E is 155 seconds, and the nitrogen-on timefor regenerator N-2 is 145 seconds. This setting of the two-way valvesis maintained until it is noted that the pressure reading of the gauge52 indicates higher than the pressure reading of the gauge El, and thenthe two-way valves 4| to i l inclusive will be turned to the positionshown in Fig. l. The air time for regenerator N-2 will then be shortenedand the nitrogen time for regenerator N-Z lengthened so that thisregenerator will gradually become unclogged.

In Fig. 1 there is illustrated a system for controlling the reversingvalves by fiuid pressure impulses. Alternatively such control can beelectrical, and apparatus for electrical control is indicateddiagrammatically and fragmentarily in Fig. 2, only the control for onereversing valve being shown. In Fig. 2 the reversing valve 22 iselectrically operated by electrically responsive means I22 which may bea solenoid device or an electric motor device. Electric power isfurnished through the lines 56 and 51, line 58 being connected by wire53 to one terminal of the motor device 522. The other line 5! isconnected by a connection 59 to one of the terminals of switches fill,there being one switch I37 associated with each cam A-i to A-4 and B-Ito B-4 inclusive. The cam followers I36 are operatively connected toswitch closing cars 50 of the switches :21.

Instead of the two-way valves ll to 44 inclusive, there are providedtwo-way switches IM to I 34 inclusive, which are connected respectivelyto the other terminal of the motor device I22 of the reversing valves bywire GI. The two switch points of switches Mi to I 44 inclusive'areconnected by wires 63 and 64 respectively to the switch I3! of the camsA and the switch I3! of the cams B. It will be seen that when the camfollower I35 contacts the high side of the cam A-I the switch I3!associated therewith will be closed by the switch bar 89 engaging theswitch points. If the two-way switch I-H contacts the switch point towhich wire 63 is connected, current will flow through the circuit fromline 51,

connection 59, switch bar 60, wire 63, switch I,

and wire 6| to the motor device I22, and then through wire 58 to theline 56. In such position of the switches MI to I44 inclusive, thereversing valves will be in control of the cams A. To place thereversing valves in control of the cams B, the switches MI to I44inclusive will be thrown to the right, so that when the cam follower I36rides on the high side of the cam B-I, current will flow from the line5! through connection 59, switch bar of the switch associated with camB-I, wire 64, switch MI, wire SI, to motor device I22, and from thencethrough wire 58 to line 56.

If desired, the shifting of the two-way valves 4| to 44 or of theswitches MI to I44 could be accomplished automatically by providing asuitable motor devic which would be operable in response to thedirection of pressure difierence between the pressures indicated by thedifferential gauges 51 and 52. It has been found, however, that theswitching of control to one set of cams or to the other set of cams needbe done only at relatively long periods, so that manual observation andcontrol will ordinarily be convenient and satisfactory. For example, aset of regenerators with the reversing periods controlled according tothe invention was operated with control according to the timing providedby the cams B. Thus the flow of nitrogen through regenerator N-I islonger, and the flow of incoming air through regenerator N-2 is longer,and regenerator N-I would tend. to become cleared of any carbon dioxideaccumulation. From onethirty to two oclock, regenerator N-I showed aslightly higher pressure drop than regenerator N-Z. At about two-thirtyo'clock, regenerator N-Z began showing a pressure drop greater than thatthrough regenerator N-I At this time control was switched to the cams A.At about threethirty both regenerators were operating at the samepressure drop. At four-thirty, regenerator N-I began to have a slightlyhigher pressure drop than regenerator N-2, and control was switched tocams B. At about six-thirty the pressure drop through both regeneratorswas equal, which condition continued until about nine oclock, whencontrol was shifted back to cams A. Thus it is seen that only a fewoperations are required during a twelve-hour period and that the lengthof time for operation under control of one set of cams is notnecessarily the same as th length of time under control of the other setof cams.

With the method of operation according to the invention, theregenerators have been in operation for indefinite periods of timewithout any diiiiculty due to clogging. It has also been found thatclogging of one or the other of a pair of regenerators tended to occurirrespective of other means employed for unbalancing the regenerators,such as a bleeding off from an intermediate portion of the regeneratorsof a portion of the air before such portion has deposited its carbondioxide, and the provision of the outfiowing gas at such a temperaturethat the carbon dioxide deposited in the coldest part of th regeneratorwill have sufficient vapor pressure so that it may be revaporized.

The above-described control of the flow time periods of the reversingcycle may be also employed for the operation of a second set ofregenerators employed to cool incoming air by a gaseous oxygen productin a plant that produces gaseous oxygen as well as eifiuent nitrogen. Insome large plants the regenerators for cooling ,air by one of theproducts comprise more than two, for example four, six, or eightregenerators comprise a set. In such cases one-half the regenerators ofa set will be controlled and operated in parallel similarly toregenerator N-! and the other half of the regenerators will be operatedin parallel similarly to regenerator N-2. Onehalf the parallel operatingregenerators may be controlled by a common reversing valve 22 or 23 forair and a common reversing valve 2 or 25 for outgoing product and theunbalancing of the flow time periods may be effected as described abovein connection with regenerators N-l and N-2. Smaller reversing valvescan be employed by using individual reversing valves for each paralleloperating regenerator and then the timing control system will be similaras to cams and twoway valves 4! to 44 of Fig. 1 but differ only inproviding branches of the pressure impulse lines 45 to 4-8 sufficient tosimultaneously control the individual reversing valves of each group ofparallel operating regenerators.

For carryin out the method of deliberate un" balance by keeping thehalf-periods of the reversing cycle constantly equal and effectindeliberate iiow restrictions, the customary reversing valve mechanismproviding equal times may be employed and there may be added suitablefiow restricting means such as partial shut-ofi valves in the pipesconducting air into or out of each regenerate-r or in the pipesconductin the cold product into or out of each regenerator. An exampleof such a control is illustrated in Fig. 3 as applied, to outgoingnitrogen. Only the lower ends of regenerators N-l and N-Z are shown asthe control mechanism of the upper ends is the customary type providingequal half-periods of flow for air and nitrogen. lhe piping at the loweror cold ends is similar to that at the lower part of Fig. l, but at thejunction of conduits [5, ll, and is there is diagrammaticallyillustrated a two-way restriction device 66. This may be similar to atwo-way plug valve having a rotor 61 that never cuts ed the openin toconduit 16 but has a flow-restricting segment 68 opposite conduit 16.The rotor is turnable by a laterally extending operator handle 89through a limited are as determined by adjustable limit stops 16 and Hthat are positioned to engage the handle 69 when it is in either extremeposition. When the handle 6% contacts stop iii the segment 88 partiallyrestricts the passage between conduits l6 and H while allowing freepassage between conduits l3 and E "When the handle t9 contacts stop Hthe segments as partially restricts flow betwen conduits it and I8 andallows free flow between conduits l and ll.

With the device 66 positioned as shown in Fig. 3, regenerator N-i willreceive less outflowing nitrogen during it nitrogen flow half-periodsthan regenerator N-2 and, since the air flows are substantially equal,regenerator N-2 will positively clear itself of deposits while reenerator N-l will tend to clog. When such clogging is definitelyindicated by pressure drop measurements, the device 56 is shifted to theopposite position to effect clearing of regenerator N-l with eventualclogging of regenerator I T-2.

It will be seen that a slight back pressure may build up only during thehalf-period of nitrogen flow through that regenerator through which theflow is restricted. Such back pressure surge is dissipated during thesucceeding half-period of the reversing cycle and causes more nitrogento flow through the regenerator that is not deliberated restricted. Theback pressure build-up or 10 surge is minimized by the volume of pipinand passages including conduit [6 and if desired such volume can beincreased by providing an enlargement or surge chamber in or connectedto the conduit it. The degree or" flow restriction to be effected shouldbe just definitely more by a small amount than the maximum restrictiondue to clogging by deposited material which can clearly be observed bypressure drop observations.

Alternatively, as mentioned hereinabove, a similar flow restrictiondevice may be employed to control the air supply conduits, and if theair is supplied by a rotary compressor the volumetric output of which isaffected slightly by the back pressure, no surge chamber may be needed.

A similar control by restriction of flows may be applied to the heatexchanger set for gaseous oxygen product in plants producing gaseousoxygen. In such case it will be preferable to arrange the reversalcycles of the nitrogen passage pair and the oxygen passage pair so thatwhen the air for the nitrogen pair is on the restricted half-period, theair for the oxygen pair is on the unrestricted half-period to minimizeback pressure surge effects.

When two or more parallel operating regenerators form one-half of theregenerators of a set for warming an outgoing product, the method ofunbalance by flow restrictions can also be employed. This is illustratedin Fig. 4 as applied to the outgoing product warmed in a set of fourregenerators P4, P-2, P-3, and P-d. These have iping and reversingvalves at their warm ends providing equal half-periods of reversin cycleand so that air flows in through regenerators P-i and P4 while productgas flows out through regenerators P-3 and P-4 during one half-periodand during the other half-period the flows are reversed.

At the cold ends shown in Fig. 4, the air outlet connections areconventional except that connection 5 it has branches l2 and i3connecting to reenerators P-! and P2 and connection H4 has branches hiand connecting to regenerators P-3 and P-t. During one half-period airpasses out through branches l2 and i3, connection H3, check valve I25 tocold air outlet conduit H5, and durin the other half-period air passesout through branches 14 and I5, connection H4, check valve l 21, toconduit ll 5.

The outgoing product supplied at conduit H5 flows as permitted by thereversing valves at the warm ends either through check valve 128 andconnection H? to the inlet of a two-way restriction device M6 or throughcheck valve I29 and connection H8 to a two-way restriction device 266.These devices may be similar to that shown at (iii in Fig. 3 havingrotor segments U38 and 268 movable by operator arms H69 and 2% to eitherof two extreme positions, one such position being illustrated in Fig. 4.The side outlets of the devices 5% and 256 are connected by conoluits l!and i8 respectively to the regenerators P-l and P2 and by conduits IE3and 8!) to the regenerators P-3 and P-4. Limit stops may also beprovided, for example, adjustable stops S3 and B4, and 86 may limit themovement of the arms I59 and 269 respectively to provide the desiredamount of flow restriction through the devices E66 and 265 fromconnections Ill and H3 to conduits Ti and 79 respectively in thepositions shown in Fig. 4 and when the arms 59 and ass are moved to theother limits 34 and 85, toprovide the desired flow restriction from V 11connections I l1 and H 8 to conduits H3 and 89 respectively.

In a preferred method of operation of a duplicate set or" regenerators,the flow of air to the regenerators P-! and P-2 at the warm ends will bebalanced as closely as possible to the flow of air to regenerators P-3and P4 by the addition of a slight flow restriction as required to makethe total flow resistance the same on either setting of the reversingvalves when the regenerators are clean.

With the positions shown in Fig. 4, and during the half-periods whenproduct flows through regenerators P! and P-Z, the regenerator P-2 willreceive more outflowing product than regenerator P-l so that regeneratorP-l will have a tendency to clog. Also regenerator 'P-A receives moreoutflowing product than regenerator P-3 during the remaininghalf-periods, so that regenerator P-3 will have the tendency to clogwhile regenerators P-2 and P- l will tend to become cleared of anyaccumulated deposits. When, after operating as shown in Fig. 4 for anindefinite time, regenerator P4 or P-3 may indicate clogging, then thedevice 166 or device 266 is switched. Ii device IE6 is switched,regenerator P-l will become positively cleared while regenerator P-2will then tend to clog. If at a diiferent time regenerator P-3 showsexcessive pressure drop, device 266 is switched, causing regenerator P-3to become positively cleared, while regenerator P-4 will tend to clog.

A similar flow-restricting control may be used alternatively in the airconduits when multiple regenerators are employed and the benefits willbe similar. Instead of controlling by flow resistance unbalance, a setof multiple regenerators may be controlled by the method of unequal flowperiods. With equal time periods, the reversing valves for outgoingproduct, for example flowing from regenerators P-l and P42, would beopen simultaneously for the outgoing product half-period, but todeliberately restrict flow through regenerator PI and favor P-Z, thereversing valve for regenerator P-l may be controlled to open a littlelater and close a little earlier than the reversing valve forregenerator P-2. When regenerator P-l indicates clogging, the timing ofthe two reversing valves may be switched. A similar timing control maybe applied to the reversing valves of regenerators P-3 and RA.

What is claimed is:

1. A method of preventing excess accumulation of condensible material inperiodically reversed heat exchange devices employed for cooling aninitially warm gas containing such condensible material by a cold gaswhich is initially free of the condensible material includingcondensation of material from the initially warm gas and evaporation ofmaterial into the initially cold gas, the periodic reversal beingefiected by a succession of complete reversal cycles each consisting oftwo periods during the first of which the initially warm gas flows fromthe warm end to the cold end of one of a heat exchange passage pairwhile the initially cold gas flows from the cold to the warm end of theother of the heat exchange passage pair and during the second period ofthe cycle the initially warm gas flows from the warm to the cold end ofthe other of said pair while the initially cold gas flows from the coldto the warm end of the first mentioned one of said pair, which methodcomprises causing during each complete reversal cycle of a succession ofcycles the flow of one of said gases through one of the heat exchangepassage pair to be more by a predetermined amount than through the otherof said pair until a residue of condensible material tends to clog oneof said pair; then causing the flow of said one gas through the other ofsaid pair to be more by a predetermined amount than through saidfirst-mentioned one of said pair to reduce said accumulation ofcondensible material in the partly clogged passage; and when condensiblematerial tends to clog the originally unclogged passage, repeating thefirst step.

2. A method of preventing excess accumulation of condensible material inperiodically reversed heat exchange devices according to claim 1, inwhich the unbalance of flow is effected by maintaining the periodicreversal times of the two periods of each complete reversing cyclesubstantially equal and causing the increased flow through one of thepassage pair by imposing additional resistance to flow through the otherof said pair.

3. A method of preventing excess accumulation of condensible material inperiodically reversed heat exchange devices according to claim 1, inwhich the unbalance of flow is eifected by making the flow times of thetwo periods of each complete reversing cycle unequal, such that the timeof flow of one of said gases through one of said passage pair is longerthan the time of flow of said one gas through the other of said pair.

4. A method of preventing excess accumulation or condensible material inperiodically reversed heat exchange devices employed for cooling gaseousfiuids containing such condensible material by cold gas which isinitially free of the condensible material, which method comprisesdecreasing by a predetermined amount the periodic time of flow of thecold gas through one of a heat exchange passage pair whilecorrespondingly increasing the periodic time of flow of the cold gasthrough the other of said pair until condensible material tends to clogsaid one; then switching such timing inequality to provide the shorterperiodic time of flow of the cold gas through the other of said pairthan through said one to reduce the accumulation of condensible materialin said one passage; and when condensible material tends to clog saidother passage, repeating the first step.

5. A method of preventing excess accumulation of condensible material inperiodically reversed heat exchange devices employed for cooling gaseousfluids containing such condensible material by cold gas which isinitially free of the condensible material, which method comprisesincreasing by a predetermined amount the periodic time of flow of thegaseous fluid through one of a heat exchange passage pair whilecorrespondingly decreasing the periodic time of flow of the gaseousfluid through the other of said pair until condensible material tends toclog said one; then switching such timing inequality to provide greaterperiodic time of flow of the gaseous fluid through the other of saidpair than through said one to reduce the accumulation of condensiblematerial in said one passage; and when condensible material tends toclog said other passage, repeating the first step.

6. A method of preventing excess accumulation of condensible material inperiodically reversed heat exchange devices employed for cooling gaseousfluids containing such condensible material by cold gas which isinitially free of the condensible material, which method comprisesincreasing by a predetermined amount the resistance to flow of the coldgas through one or a heat exchange passage pair so that less cold gasflows through same than through the other of said pair until condensiblematerial tends to clog said one; then removing said increased resistanceand increasing by a predetermined amount the resistance to flow of thecold gas through the other or" said pair so that less cold gas flowsthrough said other than through said one to reduce the accumulation ofcondensiole material in the one passage; and when condensible materialtends to clog said other passage, repeating the first step.

'7. A method of preventing excess accumulation of condensible materialin periodically reversed heat exchange devices employed for coolinggaseous fluids containing such condensible material by cold gas which isii'iitially free of the condensible material, which method comprisesincreasing by a predetermined amount the resistance flow of the gaseousfluid through one of a heat exchange passage pair so that less gaseousfluid flows through same than through the other of said pair untilcondensible material tends to clog said other of the pair; then removingsaid increased resistance and increasing by a predetermined amount theresistance to fiow of gaseous fluid through the other of said pair sothat less gaseous fluid flows through said other than through said oneto reduce the accumulation of condensible material in said otherpassage; and when condensible material tends to clog other passage,repeating the first step.

8. Apparatus for controlling the operation of periodically reversed heatexchange devices that cool an initially warm gas containing condensiblematerial by an initially cold gas that is initially free of suchmaterial, which apparatus com prises, in combination with gas flowreversing mechanism for periodically reversing the flow of the warm gasand the cold gas through a pair of heat exchange passages; of switchingapparatus shiftable to either of two settings and constructed andarranged, when shifted to one of said settings, to eiTect the flow of apredetermined greater amount of one of said gases through one of suchpair of passages than througl the other of said pair for a desirednumber of reversal periods and for a succeeding desired number ofreversal periods when shifted to the other of said settings, to effectthe flow of a predetermined lesser amount of said one gas through saidone passage than through said other passage.

9. Apparatus for controlling the operation of periodically reversed heatexchange devices according to claim 8 in which said reversing mechanismincludes reversing valves interposed in the gas connections at the warmends of the heat exchange passages, said valves having motor operators,and means for delivering timed motive impulses to said motor operators;and said switching apparatus comprises duplicate devices for deliveringsaid timed impulses constructed to deliver oppositely phased longer andshorter impulses, and switching means to switch control of said motoroperators to either of the duplicate impulse delivering means.

10. Apparatus for controlling the operation of periodically reversedheat exchange devices according to claim 8 in which said switchingapparatus comprises flow resistance increasing devices connected tocontrol the flow of a gas through each of said heat exchange passages;and operating means for said devices operable for increasing theresistance to flow of said one gas through said other of said pair ofpassages for said desired number of periods and for eliminating suchincreased resistance and increasing the resistance to flow of said onegas through said one passage for the succeeding number of reversalperiods.

11. Apparatus for controlling the operation of periodically reversedheat exchange devices that cool a warm gas containing condensiblematerial by a cold gas that is initially free of such material, whichapparatus comprises, in combination with reversing valves interposed ingas connections at the warm ends of a pair of heat exchange passages andoperable to periodically reverse the flow of initially warm gas andinitially cold gas through such passages, said valves having motoroperators; of means including pairs of cams all connected to be drivenat a rate corresponding to the complete reversal cycle, said cams havingtwo cam follower positioning portions of unequal length and the totallength of said two portions corresponding to a complete reversing cycle,and the follower positioning portions of the two cams constituting eachpair being oppositely related; cam followers for each cam operativelyconnected to impulse delivering means; and switching means connectedbetween the two impulse delivering means associated with each pair ofcams and one or said motor operators and operable to switch control ofthe motor operator to receive impulses from the impulse delivering meansoperated by either of the cams of a pair of cams.

12. Apparatus for controlling the operation of periodically reversedheat exchange devices that cool a warm gas containing condensiblematerial by a cold gas that is initially free of such material andincluding two sets of heat exchange passages and two or more heatexchange passages forming each set and connected together to operate asa unit, which apparatus comprises in combination with means forperiodically reversing the flow of the warm gas and the cold gasalternately through each set of heat exchange passages; flow resistanceincreasing devices connected to control the flow of a gas through eachof said heat exchange passages; and operators for said devices operableto apply added flow resistance to half the number of heat exchangepassages of a set for a desired number of reversal periods and to removesuch resistance and apply added flow resistance to the other half of theheat exchange passages of said set.

13. Apparatus for controlling the operation of periodically reversedheat exchange devices according to claim 12, which includes means forinitially balancing the flow of gas among the several heat exchangepassages.

14. Apparatus for controlling the operation of periodically reversedheat exchange devices that cool an initially warm gas containingcondensible material by an initially cold gas that is initially free ofsuch material, which apparatus comprises, in combination with gas flowreversing mechanism for periodically reversing the flow of the warm gasand the cold gas through a pair of heat exchange passages, saidmechanism comprising conduits having automatic valves controlling theflow of the cooled warm gas from and the cold gas to the cold ends ofsaid passages, motor operated valves controlling conduits at the warmends of said passages to start and stop flow of warm gas alternately toand of initially cold warmed gas alternately from said passages, andmechanism for timing the operation of said motor operated valves toefiect successive complete reversal cycles consisting of two periodsduring a first period of which the motor valve controlling flow of warmgas to one passage is open and the motor valve controlling flow of warmgas to the other passage is closed While the motor valve controllingdischarge from the one passage is closed and the motor valve controllingdischarge from the other passage is open and during the last period ofthe reversal cycle the motor valves are oppositely positioned; ofswitching apparatus associated with said gas flow reversing mechanismand shiftable to either of two settings and constructed and arrangedwhen shifted to either of said settings to unbalance the flow times ofsaid first and last periods of the reversal cycle.

15. Apparatus for controlling the operation of periodically reversedheat exchange devices that cool an initially Warm gas containingcondensible material by an initially cold gas that is initially free ofsuch material, which apparatus comprises, in combination with gas fiowreversing mechanism for periodically reversing the flow of the warm gasand the cold gas through a pair of heat exchange passages, saidmechanism comprising conduits having automatic valves controlling theflow of the cooled warm gas from and the cold gas to the cold ends ofsaid passages, motor operated valves controlling conduits at the warmends of said passages to start and stop flow of warm gas alternately toand of initially cold warmed gas alternately from said passages, andmechanism for timing the operation of said motor operated valves toeffect successive complete reversal cycles consisting of two periodsduring a first period of which the motor valve controlling flow of warmgas to one passage is open and the motor valve controlling flow of warmgas to the oth r passage is closed while the motor valve controllingdischarge from the one passage is closed and th motor valve controllingdischarge from the other passage is open and during the last period ofthe reversal cycle the motor valves are oppositely positioned; ofswitching apparatus associated with said conduits and shifts-hie toeither of two settings and constructed and arranged when shifted to oneof said settings to introduce increased resistance to flow of one ofsaid gases through one of such pair of passages than through the otherof such pair for a desired number of reversal cycles and when shifted tothe other of said settings to eliminate said increased resistance andintroduce increased resistance to flow of said one gas through the otherof said pair of passages for a succeeding desired number of reversalcycles.

References Cited in the file Of this patent UNITED STATES PATENTS NumberName Date 2,084,987 Borchardt June 29, 1937 2,553,550 Collins May 22,1951

